Home Renovations: How To Repair Damaged Stucco

Patching damaged stucco on your home's exterior can be easy, although some situations call for professional expertise.

Stucco is an exterior plastering material made up of Portland cement, lime and sand. Whether or not it can be easily repaired by the homeowner depends on a number of factors, the age of the original stucco being only one.

If you have minor cracks in your stucco, these can be easily mended with a stucco caulk and should be repaired as soon as possible, since cracks allow moisture to get in and weaken the undamaged stucco. That could cause you to have a much larger problem to deal with. Minor holes can likewise be quickly patched up with a stucco patching compound that is applied in a single layer and that won't shrink when dried. Larger areas can also be repaired with one-layer patch compound, but for authenticity, you may want to do your repairs with actual stucco material.

If your home is fairly young and you know the composition of the stucco mix that was used, matching it will be much easier. Your local home-builders supply store is a good source of information. They usually know what the local builders used in the developments in your area and can quickly identify the supplies you will need.

If you're repairing stucco in an older home, you may be unable to get the same mix and will have to approximate it. If the stucco was tinted with cement dye in the outermost layer, matching the color is probably a job for a professional. However, if you are going to paint over the stucco, matching the exact stucco brand with the original is less of an issue.

To prepare the surface for a new application of stucco, break up and knock out the entire damaged portion, up to and slightly into the non-damaged stucco. Use a chisel on an angle to cut a beveled edge around the perimeter of the hole, angling in to preserve a lip of old stucco to hold the patch in place. Use a brush or shop-vac to remove the debris from the area that needs to be patched. Dust from old stucco will prevent the new layers from adhering to the surface.

You should only work with stucco when the temperature is below 80 degrees and above 40 degrees. If working on a sunny side of the house, you will want to wait for a cloudy day so that the sun doesn't dry out your mix too quickly. Stucco is applied on top of a wire mesh or tar paper, which prevents the moisture from the wet mix from penetrating and holds it to the surface. Stucco may also be applied directly onto concrete or brick walls. Follow the directions to make your mix. Only make as much as you can apply in an hour or so, since it will harden as you work.

Stucco is applied in three layers. Use a 'float' to apply and smooth a three-eighths of an inch layer of stucco mix into the area to be patched. Make sure to get it under the lip you've preserved in the old material, and press it to ensure that it bonds with the backing. Smooth over it to make sure your layer is of a consistent depth. Then use a 'comb' of nails to carve grooves in the surface. These grooves will ensure that the next layer will bond to the first one.

Let the first layer cure for one to three days before applying the next layer; keep the patch damp by misting it with water if necessary. Drying too quickly will cause the stucco to crack and shrink. Then apply the second layer in the same way as the first. The final layer is thinner, only an eighth of an inch; it is this layer to which any texture will be applied. You can apply texture to the completed patch by making arcs with your float or by flatly dragging a board down the surface, depending on the texture you are matching.

If you are repairing painted stucco, allow your new application to cure for thirty days before painting the patch. If you are restoring a historic home and are not a professional, you probably should consult one, whether or not you choose to do the work yourself.